Size Effect of Au Nanoparticles on TiO2Crystalline Phase of Nanocomposite Thin Films and Their Photocatalytic Properties

This work focuses on the size effects of Au nanoparticles (AuNPs) on the TiO2 crystalline phase of nanocomposite AuNPs-embedded TiO2 (Au-TiO2) thin films, their adsorption ability, and photocatalytic activity. Au-TiO2 films were synthesized through a sol-gel method using polyvinylpyrrolidone-protected AuNPs (AuNPs@PVP). The mean diameters of AuNPs@PVP dispersed in a sol solution were 2.0±0.7 or 7.9±3.1 nm and the heat-treatment temperature of the films was 400-900 °C. XRD and Ti L3,2-edge X-ray absorption near-edge structure (XANES) analysis revealed that AuNPs doping could suppress an anatase to rutile phase transformation. In addition, the larger size of AuNPs doped in TiO2 film tended to prevent the transformation more effectively. The film doped with the smaller AuNPs@PVP and annealed at 500 °C showed the highest photocatalytic activity among the obtained films because it had the well crystallized anatase phase and the high adsorption ability, which was attributed to the existence of a five-coordinated Ti site that was revealed from Ti K-edge XANES measurements.